1. Field of the Invention
The present invention relates to an apparatus for comminuting material with a separate air supply.
2. Description of the Background Art
Devices of this class are characterized by an air-ventilated mode of operation. Air, together with a mixture of gaseous and solid materials, is thereby axially channeled into a comminuting room, and after radial rerouting is conveyed by centrifugal forces to an annular comminuting zone, where it is comminuted between the comminuting tools to a desired size. After exiting the comminuting zone, the suitably milled material gathers in a ring channel, which is located between the housing and the comminuting tools, where it is tangentially discharged by the air stream via the material discharge. Apart from the centrifugal forces, the driving force for the transport of the material through the comminuting apparatus is essentially the air flow, the sweeping force of which affects the material.
When the material is comminuted in the comminuting zone, a considerable part of the energy required for the comminuting is converted into heat. This is caused by friction and impact forces the material is subjected to during comminuting, which primarily affect the comminuting tools. The heating up of the material resulting therefrom carries the risk on the one hand, particularly with regard to heat-sensitive materials and/or fine and finest-milled materials, of the material to be irreversibly ruined, and on the other hand, of the comminuting device to suffer damage due to thermal stress.
Conventionally, the cooling of devices of this class is done via the air portion in the mixture of gaseous and solid materials that passes through the milling gap. A heat transfer from the comminuting tools to the air thereby takes place, whereby the desired cooling effect is achieved. Thus, devices of this class are characterized in that during the comminuting operation, the air flowing through the device has a transport function as well as a cooling function.
Furthermore, it is known to channel additional air into the comminuting room. The additional air volume is able to remove heat, thus increasing the cooling effect. Again, the heated air is discharged together with the suitably milled material.
The disadvantage of conventional comminuting devices is the dual function of the mixture of gaseous and solid materials, which on the one hand has the task of transporting the material, and on the other hand has the task of cooling. Under certain circumstances, for example, in the case of fine and finest milling, the air portion in the mixture must be increased beyond the volume needed for transport for reasons of cooling. As a consequence, large volumes must be filtered to separate the milled material from the mixture of gaseous and solid materials exiting the device. From a structural-technical point of view, this requires large filter surfaces and large conduit cross sections, which, apart from high investment and operation costs, also has the additional consequence of increased spatial requirements.
This disadvantage is also a characteristic of devices of this class, where additional cool air is channeled in because upstream to the comminuting zone, the additional cool air merges with the mixture of gaseous and solid materials.
Furthermore, only as an exception does the dual function of the mixture of gaseous and solid materials during the comminuting process lead to an optimal utilization of the comminuting device. In most cases, either the conveying potential of the air portion in the mixture of gaseous and solid materials is exhausted while there are still cooling reserves, or the cooling potential of the air portion is exhausted, although reserves in the conveying capacity would still be available. This leads to a diminished efficiency of conventional devices.